1. Field of the Invention
The present invention relates to a blood pressure measuring apparatus and particularly to the art of preventing or eliminating retention of venous blood and thereby improving accuracy of blood pressure measurement.
2. Related Art Statement
Before or after a surgical operation, a patient needs to rest on a bed without moving his or her superior or inferior limbs for a long time. If the patient does not move his or her superior or inferior limbs for a long time, then blood tends to stay in large venous sinuses that are present in muscles and are free of valves. Normally, the contractions of the muscles send the blood staying in the veins, back to the proximal side, i.e., the heart. In a special case, however, in which the patient""s muscle forces are not so strong, the blood cannot flow so fast and accordingly tends to stay in the veins. In particular, blood is likely to stay in veins of legs.
If blood pressure values are measured from a portion of the patient in which venous blood stays, an accurate diastolic blood pressure cannot be measured. Since, however, a conventional blood pressure measuring apparatus measures blood pressure values without taking into account whether blood stays in veins, an accurate diastolic blood pressure may not be obtained.
It is therefore an object of the present invention to provide a blood pressure measuring apparatus which can measure an accurate blood pressure from a portion of a living subject that suffers retention of venous blood.
The above object has been achieved by the present invention. According to a first feature of the present invention, there is provided an apparatus for measuring a blood pressure of at least one of a superior limb and an inferior limb of a living subject, comprising a blood-pressure measuring device which includes a measuring member adapted to be worn on a measurement portion of said one of the superior and inferior limbs and measures a blood pressure of the measurement portion; and a pressing device which includes a pressing member adapted to be worn on a pressed portion of the subject that comprises at least one of the measurement portion and a distal portion of the subject relative to the measurement portion, and which presses the pressed portion with a prescribed blood-flow promoting force that is lower than a systolic blood pressure of the subject.
According to this invention, the pressing device presses the blood-pressure measurement portion of the subject or the distal portion of the subject relative to the measurement portion, and then stops pressing the measurement or distal portion. Consequently, flow of blood is promoted in veins of the measurement portion on which the measuring member is worn and a proximal portion of the subject relative to the measurement portion. Therefore, even if the measurement or proximal portion may suffer retention of venous blood, the retention can be eliminated. That is, since the pressing device presses the measurement or distal portion of the subject and then stops pressing the portion, the present apparatus can measure an accurate blood pressure of the subject.
According to a second feature of the present invention that includes the first feature, the pressing device further comprises pressing means for controlling, before the blood-pressure measuring device starts measuring the blood pressure of the measurement portion, the pressing member to first press the pressed portion with the blood-flow promoting force and then decrease the blood-flow promoting force.
The pressing means may control the pressing member such that immediately before the blood-pressure measuring device starts measuring the blood pressure of the measurement portion, the pressing member presses the pressed portion of the subject. Alternatively, the pressing means may control the pressing member such that before the blood-pressure measuring device starts measuring the blood pressure, the pressing member periodically presses the pressed portion of the subject at a prescribed period.
According to the first feature, the pressing device may be one which is manually operated to press the measurement portion of the subject. In this case, if an operator can judge that the measurement portion does not suffer retention of venous blood (e.g., because the subject is very young), an accurate blood pressure can be measured without having to operating the pressing device to press the measurement portion with the blood-flow promoting force. In this case, however, the pressing operation of the pressing device must be initiated by a different action of the operator than an action needed to initiate the blood-pressure measuring operation. Thus, the manually operable pressing device is less easy to use than the pressing device according to the second feature. In addition, the operator may erroneously initiate the blood pressure measuring operation without initiating the pressing operation of the manually operable pressing device, where the pressing operation is needed. In this case, an inaccurate blood pressure may be measured. In contrast, according to the second feature, the pressing means automatically eliminates retention of venous blood before commencement of the blood-pressure measuring operation. Thus, the present apparatus can be easily operated and can measure an accurate blood pressure of the subject.
According to a third feature of the present invention that includes the first or second feature, the measuring member of the blood-pressure measuring device comprises an inflatable cuff which is adapted to be worn on the measurement portion of the one of the superior and inferior limbs, and the pressing member of the pressing device comprises the inflatable cuff.
According to this feature, the cuff as part of the blood-pressure measuring device is used as part of the pressing device, and it is not needed to employ an exclusive pressing member in addition to the cuff.